Problem: In 36 years, Luis will be 4 times as old as he is right now. How old is he right now?
Explanation: We can use the given information to write down an equation about Luis's age. Let Luis's age be $l$ In 36 years, he will be $l + 36$ years old. At that time, he will also be $4 l$ years old. Writing this information as an equation, we get: $l + 36 = 4 l$ Solving for $l$ , we get: $3 l = 36$ $l = 12$.